Waterborne dispersions of epoxidized polydiene block copolymers and amino resins

ABSTRACT

A crosslinkble waterborne dispersion useful as a coating on metal substrates of an epoxidized polydiene block polymer composition which comprises: (a) 10 to 65% by weight of a polydiene block polymer containing at least five olefinic epoxy groups per molecule which are sterically hindered, (b) 0.2 to 25% by weight of a compatible aminoplast, (c) 0.1 to 10% by weight of a surfactant which is nonionic or anionic and has a volatile cation, and (d) the balance water. A water-continuous process and an inversion process for making a dispersion are also described.

This is a division, of application Ser. No. 08/262,818, filed Jun. 21,1994 abandoned.

BACKGROUND OF THE INVENTION

This invention relates to waterborne dispersions of epoxidized polydieneblock polymers. More specifically, the invention relates to waterbornedispersions of such polymers and amino resins which can be crosslinkedto make cured films, coatings, adhesives, sealants, caulks, binders andmodifiers for asphalt.

Epoxidized polydiene polymers have been disclosed recently in U.S. Pat.Nos. 5,229,464 and 5,247,026. These are relatively low epoxy contentpolymers. Higher epoxy content polymers are described in copending,commonly assigned United States patent application Ser. No. 228,047,filed Apr. 15, 1994, entitled “Epoxidized Low Viscosity Rubber.” It hasbeen shown that such polymers are useful in high solids, solvent-borneadhesives and coatings and that formulations containing these polymersand a cationic photoinitiator can be cured via ultraviolet radiation. Ithas also been shown that formulations containing these polymers, amelamine resin, and an acid catalyst can be cured by baking under normalbake conditions.

Although this high solids technology is of great value, it is true thatif such polymers could be dispersed in water, the utility of thesepolymers would be greatly broadened. This would allow preparation of lowviscosity, waterborne formulations having very low volatile organiccompound (VOC) contents. By adding waterborne epoxidized polydienepolymer dispersions to other water-based products having compatiblesurfactant systems, these polymers could be used to modify other typesof resins and this could be done without concern about phase separationdue to incompatibility of the epoxidized polydiene polymers andsolvent-based resins.

It is one object of the present invention to provide a crosslinkablewaterborne dispersion of epoxidized polydiene polymers and amino resins.Another object of this invention is to provide a method for maldng suchcrosslinkable waterborne dispersions.

SUMMARY OF THE INVENTION

The present invention provides a water dispersion of a crosslinkableepoxidized polydiene block polymer composition which comprises:

(a) 10 to 65% by weight (% w) of a polydiene block polymer containing atleast 5 olefinic epoxy groups per molecule which are sterically hinderedand which preferably do not have a significant amount of otherfunctional groups,

(b) 0.2 to 25% w of a compatible amino resin,

(c) 0.1 to 10% w of a nonionic surfactant or an anionic surfactanthaving a volatile cation, and

(d) the balance water.

In a preferred embodiment of the present invention, the compatibleaminoplast is a butylated aminoplast and the surfactant is an anionicsurfactant composed of an amine salt of an acid which can be used tocatalyze the crosslinldng of the polymer and the aminoplast such asparatoluene sulfonic acid or dodecylbenzene sulfonic acid.

This invention also describes processes for making such crosslinkablewaterborne dispersions. One method involves making a hot aqueoussolution of the surfactant, adding a mixture of an epoxidized blockpolymer and a compatible aminoplast to the hot aqueous solution, andthen mixing the components under high shear conditions. The preferredmethod involves mixing together at a temperature of 25 to 90° C. withvigorous agitation an epoxidized polydiene block polymer, an aminoplast,and the desired surfactant, and then adding water to the mixture slowlyover a period of at least 15 minutes.

DETAILED DESCRIPTION OF THE INVENTION

The general methods of making block copolymers are reviewed by R. P.Quirk and J. Kim, “Recent Advances in Thermoplastic ElastomerSynthesis,” Rubber Chemistry and Technology, volume 64 No. 3 (1991),which is incorporated herein by reference. Especially useful is themethod of sequential anionic polymerization of monomers. The types ofmonomers that will undergo living polymeriation are relatively limitedfor the anionic method, with the most favorable being conjugateddiolefins and monoalkenyl aromatic hydrocbon monomers. Generally, ahydrogenation step is needed to prepare a saturated polymer. Hence, apolymer of this invention that is both epoxidized and saturated usuallyrequires both an epoxidation and a hydrogenation step. However, polymersmade by sequential polymerization of a suitable diolefin monomer and amonomer having only one carbon carbon double bond or by sequentialpolymerization of two different mixtures (ratios) of such monomers,using either a monofunctional initiator, a monofunctional initiator anda coupling agent, or a multifunctional initiator, may be epoxidized andwould not have to be hydrogenated to produce an epoxidized polymer ofthis invention that is saturated. Preferred polymers for use herein aredescribed in detail in the aforementioned U.S. patents and patentapplication which are herein incorporated by reference.

The polymers containing olefinic unsaturation or both aromatic andolefinic unsaturation may be prepared using anionic initiators orpolymerization catalysts. Such polymers may be prepared using bulk,solution or emulsion techniques. Polymers prepared in solution arepreferred for subsequent epoxidation and hydrogenation.

The polymer may be epoxidized under conditions that enhance theepoxidation of the more highly substituted olefinic double bonds, suchas by the use of peracetic acid, wherein the rate of epoxidation isgenerally greater the greater the degree of substitution of the olefinicdouble bond (rate of epoxidation:tetrasubstituted>trisubstituted>disubstituted>monosubstituted olefinicdouble bond). If a substantially saturated polymer is desired, theepoxidized polymer may be hydrogenated to remove substantially allremaining olefinic double bonds (ODB) and normally leaving substantiallyall of the aromatic double bonds. If only substantially saturatedinterior blocks are desired, the epoxidized polymer may be partiallyhydrogenated in a selective manner with a suitable catalyst andconditions (like those in Re 27,145, U.S. Pat. No. 4,001,199 or with atitanium catalyst such as is disclosed in U.S. Pat. No. 5,039,755, allof which are incorporated by reference; or by fixed bed hydrogenation)that favor the hydrogenation of the less substituted olefinic doublebonds (rate or hydrogenation:monosubstituted>disubstituted>trisubstituted>tetrasubstituted olefinicdouble bonds) and also leaves aromatic double bonds intact

In general, when solution anionic techniques are used, conjugateddiolefin polymers and copolymers of conjugated diolefins and alkenylaromatic hydrocarbons are prepared by contacting the monomer or monomersto be polymerized simultaneously or sequentially with an anionicpolymerization initiator such as group IA metals, their alkyls, amides,silanolates, napthalides, biphenyls and anthracenyl derivatives. It ispreferred to use an organo alkali metal (such as sodium or potassium)compound in a suitable solvent at a temperature within the range fromabout −150° C. to about 300° C., preferably at a temperature within therange from about 0° C. to about 100° C. Particularly effective anionicpolymerization initiators are organo lithium compounds having thegeneral formula:

RLi_(n)

wherein R is an aliphatic, cycloaliphatic, aromatic or alkyl-substitutedaromatic hydrocarbon radical having from 1 to about 20 carbon atoms andn is an integer of 1 to 4.

Conjugated diolefins which may be polymerized anionically include thoseconjugated diolefins containing from about 4 to about 24 carbon atomssuch as 1,3-butadiene, isoprene, piperylene, methylpentadiene,phenylbutadiene, 3,4-dimethyl-1,3-hexadiene, 4,5-diethyl-1,3-octadieneand the like. Isoprene and butadiene are the preferred conjugated dienemonomers for use in the present invention because of their low cost andready availability. The conjugated diolefins which may be used in thepresent invention include isoprene (2-methyl-1,3-butadiene),2-ethyl-1,3-butadiene, 2-propyl-1,3-butadiene, 2-butyl-1,3-butadiene,2-pentyl-1,3-butadiene(2-amyl-1,3-butadiene),2-hexyl-1,3-butadiene,2-heptyl-1,3-butadiene,2-octyl-1,3-butadiene,2-nonyl-1,3-butadiene,2-decyl-1,3-butadiene,2-dodecyl-1,3-butadiene,2-tetradecyl-1,3-butadiene, 2-hexadecyl-1,3-butadiene,2-isoamyl-1,3-butadiene, 2-phenyl-1,3-butadiene,2-methyl-1,3-pentadiene, 2-methyl-1,3-hexadiene,2-methyl-1,3-heptadiene, 2-methyl-1,3-octadiene,2-methyl-6-methylene-2,7-octadiene (myrcene), 2-methyl-1,3-nonyldiene,2-methyl-1,3-decyldiene, and 2-methyl-1,3-dodecyldiene, as well as the2-ethyl, 2-propyl, 2-butyl, 2-pentyl, 2-hexyl, 2-heptyl, 2-octyl,2-nonyl, 2-decyl, 2-dodecyl, 2-tetradecyl, 2-hexadecyl, 2-isoamyl and2-phenyl versions of all of these dienes. Also included are1,3-butadiene, piperylene, 4,5-diethyl-1,3-octadiene and the like.Di-substituted conjugated diolefins which may be used include2,3-dialkyl-substituted conjugated diolefins such as2,3-dimethyl-1,3-butadiene,2,3-diethyl-1,3-pentadiene,2,3-dimethyl-1,3-hexa-diene,2,3-diethyl-1,3-heptadiene, 2,3-dimethyl-1,3-octadiene and the like and2,3-fluoro-substituted conjugated diolefins such as2,3-difluoro-1,3-butadiene, 2,3-difluoro-1,3-pentadiene,2,3-difluoro-1,3-hexadiene, 2,3-difluoro- 1,3-heptadiene,2,3-fluoro-1,3-octadiene and the like. Alkenyl aromatic hydrocarbonswhich may be copolymerized include vinyl aryl compounds such as styrene,various alkyl-substituted styrenes, alkoxy-substituted styrenes, vinylnapthalene, alkyl-substituted vinyl napthalenes and the like.

There are a wide variety of coupling agents or initiators that can beemployed. Any polyfunctional coupling agent which contains at least tworeactive sites can be employed. Examples of the types of compounds whichcan be used include the polyepoxides, polyisocyanates, polyimines,polyaldehydes, polyketones, polyanhydrides, polyesters, polyhalides, andthe like. These compounds can contain two or more types of functionalgroups such as the combination of epoxy and aldehyde groups, isocyanateand halide groups, and the like. Many suitable types of thesepolyfunctional compounds have been described in U.S. Pat. Nos.3,595,941; 3,468,972; 3,135,716; 3,078,254; 4,096,203 and 3,594,452which are herein incorporated by reference. When the coupling agent hastwo reactive sites such as dibromoethane, the polymer will have a linearA—B—A structure. When the coupling agent has three or more reactivesites, such as silicon tetrachloride, the polymer will have a branchedstructure, such as (A—B)_(n)—X. Coupling monomers are coupling agentswhere several monomer units are necessary for every chain end to becoupled. Divinylbenzene is the most commonly used coupling monomer andresults in star polymers.

In general, any of the solvents known in the prior art to be useful inthe preparation of such polymers may be used. Suitable solvents, then,including straight- and branched chain hydrocarbons such as pentane,hexane, heptane, octane and the like, as well as, alkyl-substitutedderivatives thereof; cycloaliphatic hydrocarbons such as cyclopentane,cyclohexane, cycloheptane and the like, as well as alkyl-substitutedderivatives thereof; aromatic and alkyl-substituted aromatichydrocarbons such as benzene, naphthalene, toluene, xylene and the like;hydrogenated aromatic hydrocarbons such as tetralin, decalin and thelike; linear and cyclic ethers such as methyl ether, methylethyl ether,diethyl ether, tetrahydrofuran and the like.

More specifically, the polymers of the present invention are made by theanionic polymerization of conjugated diene monomers and alkenyl aromatichydrocarbon monomers in a hydrocarbon solvent at a temperature between 0and 100° C. using an alkyl lithium initiator. The living polymer chainsare usually coupled by addition of divinyl monomer to form a starpolymer. Additional monomers may or may not be added to grow more armsor to terminally functionalize and the polymer and the living chain endsare quenched with a proton source such as methanol or hydrogen.Polymerization may also be initiated from monomers such asm-divinylbenzene and m-diisopropenylbenzene treated with butyl lithium.

The epoxidized block copolymers may have weight average molecularweights of from about 2,000 to about 3,000,000. Lower molecular weightsrequire excessive crosslinking whereas higher molecular weights causevery high viscosity, making processing very difficult. More preferably,the polymer is one having a weight average molecular weight of fromabout 3,000 to about 1,000,000. Most preferably, the polymer is onehaving a weight average molecular weight of from about 4,000 to about200,000 because this offers the best balance between cost, ability touse the mildest curing conditions and achieving good processingbehavior. It is preferred that the blocks comprising predominantlyepoxidized diolefin monomer units have molecular weights between about200 and about 200,000 and, if present, the blocks comprisingpredominantly aromatic monomer units have molecular weights betweenabout 500 and about 50,000 because polymers built from larger blocks arevery difficult to process and smaller blocks fail to adequatelycrosslink.

Molecular weights of linear polymers or unassembled linear segments ofpolymers such as mono-, di-, triblock, etc., arms of star polymersbefore coupling are conveniently measured by Gel PermeationChromatography (GPC), where the GPC system has been appropriatelycalibrated. For polymers of the type described herein, the suitablecalibration standards are narrow molecular weight distributionpolystyrene polymers. For anionically polymerized linear polymers, thepolymer is essentially monodisperse and it is both convenient andadequately descriptive to report the “peak” molecular weight of thenarrow molecular weight distribution observed. The peak molecular weightis usually the molecular weight of the main species shown on thechromatograph. For materials to be used in the columns of the GPC,styrene-divinyl benzene gels or silica gels are commonly used and areexcellent materials. Tetrahydrofuran is an excellent solvent forpolymers of the type described herein. Ultraviolet or refractive indexdetectors may be used.

Measurement of the true molecular weight of a coupled star polymer isnot as straightforward or as easy to make using GPC. This is because thestar shaped molecules do not separate and elute through the packed GPCcolumns in the same manner as do the linear polymers used for thecalibration. Hence, the time of arrival at an ultraviolet or refractiveindex detector is not a good indicator of the molecular weight. A goodmethod to use for a star polymer is to measure the weight averagemolecular weight by light scattering techniques. The sample is dissolvedin a suitable solvent at a concentration less than 1.0 gram of sampleper 100 milliliters of solvent and filtered using a syringe and porousmembrane filters of less than 0.5 microns pore size directly into thelight scattering cell. The light scattering measurements are performedas a function of scattering angle, polymer concentration and polymersize using standard procedures. The differential refractive index (DRI)of the sample is measured at the same wave length and in the samesolvent used for the light scattering. The following references areherein incorporated by reference:

1. Modern Size-Exclusion Liquid Chromatography, M. W. Yau, J. J.Kirkland, D. D. Bly, John Wiley and Sons, New York, N.Y., 1979.

2. Light Scattering From Polymer Solutions, M. B. Huglin, ed., AcademicPress, New York, N.Y., 1972.

3. W. K. Kai and A. J. Havlik, Applied Optics, 12, 541 (1973).

4. M. L. McConnell, American laboratory, 63, May, 1978.

The epoxidized copolymers of this invention can be prepared by theepoxidation procedures as generally described or reviewed in theEncyclopedia of Chemical Technology 19, 3rd ed., 251-266 (1980), D. N.Schulz, S. R. Turner, and M. A. Golub, Rubber Chemistry and Technology,5, 809 (1982), W-K. Huang, G-H. Hsuie, and W-H. Hou, Journal of PolymerScience. Part A: Polymer Chemistry, 26, 1867 (1988), and K. A.Jorgensen, Chemical Reviews, 89, 431 (1989), and Hermann, Fischer, andMarz, Angew. Chem. Int. Ed. Engl. 30 (No. 12), 1638 (1991), all of whichare incorporated by reference.

For instance, epoxidation of the base polymer can be effected byreaction with organic peracids which can be preformed or formed in situ.Suitable preformed peracids include peracetic and perbenzoic acids. Insitu formation may be accomplished by using hydrogen peroxide and a lowmolecular weight carboxylic acid such as formic acid. Alternatively,hydrogen peroxide in the presence of acetic acid, or acetic anhydrideand a cationic exchange resin, will form a peracid. The cationicexchange resin can optionally be replaced by a strong acid such assulfuric acid or p-toluenesulfonic acid. The epoxidation reaction can beconducted directly in the polymerization cement (polymer solution inwhich the polymer was polymerized) or, alternatively, the polymer can beredissolved in an inert solvent such as toluene, benzene, hexane,cyclohexane, methylenechloride and the like and epoxidation conducted inthis new solution or can be epoxidized neat. Epoxidation temperatures onthe order of 0 to 130° C. and reaction times from 0.1 to 72 hours may beutilized. When employing hydrogen peroxide and acetic or formic acidtogether with a catalyst such as sulfuric acid, the product can be amixture of epoxide and hydroxy ester. Due to these side reactions causedby the presence of an acid and to gain the maximum selectivity withrespect to different levels of substitution on the olefinic doublebonds, it is preferable to carry out the epoxidation at the lowestpossible temperature and for the shortest time consistent with thedesired degree of epoxidation. Epoxidation may also be accomplished bytreatment of the polymer with hydroperoxides or oxygen in the presenceof transition metals such as Mo, W, Cr, V and Ag, or withmethyl-trioxorhenium/hydrogen peroxide with or without amines present.¹H NMR is an effective tool to determine which and how much of each typeof ODB is epoxidized.

Although epoxide functionality is predominant in the polymers of thepresent invention, the polymers may also contain small amounts offunctional groups that are normally considered necessary for amino resincrosslinking—i.e. groups containing active protons such as hydroxy,carboxy, mercaptan, and amine. Quantitizing what constitutes a smallamount of functional groups is difficult at best because of differencesamong various amino resins, acids, polymers, the level of these in agiven formulation, the type of functional group, the conditions of cure,etc. Also complicating the matter is the degree of cure required by theenduse application. Only a high polymer gel content may be needed toimpart a needed property, or both high gel content and a significantcrosslink density, enough to prevent appreciable swelling by a goodsolvent, may be needed. Despite these complications, the amount offunctional groups other than epoxide groups will usually be less than0.1 meq/gm.

Any polymer containing at least five olefinic epoxy groups per moleculewhich are sterically hindered may be crosslinked according to thepresent invention. Amino resin crosslinking will most likely take placeas long as there are some sterically hindered olefinic epoxy groupspresent on the polymer. It is best that there be at least five suchgroups present on the polymer to insure that there are any at all. Inanionic polymerization, it is difficult to consistently place less than5 diene monomers on a molecule. Useful products may be made frompolymers containing from 5 sterically hindered epoxy groups per moleculeto as many as 250 sterically hindered epoxy groups per molecule.

Sterically hindered means the olefinic epoxy groups are di-, tri- ortetra-alkyl substituted. Tri- and tetra-alkyl substitution is preferred.This is described in detail in copending, commonly assigned U.S. patentapplication Ser. No. 08/081,950, filed Jun. 22, 1993, entitled “Methodof Chemically Crosslinking Sterically Hindered Epoxidized Polymers”which is herein incorporated by reference.

Polymers having epoxy groups of the following structures are preferred:

where R₁ and R₂ are selected from the group consisting of hydrogen,alkyl, alkenyl, and aryl,

where R₁, R₂, R₃ and R₄ are selected from the group consisting ofhydrogen, alkyl, alkenyl and aryl and at least one of R₂, R₃ and R₄ isnot hydrogen and R₅ is selected from the group consisting of alkyl,alkenyl and aryl.

A specific example is a polymer made from 1,3-isoprene monomer such thatepoxidized 1,4-isoprene units are produced. An epoxidized 1,4-isopreneunit contains structural feature 1 where R₁ is hydrogen and R₂ is CH₃.

Another example is an isoprene based polymer where epoxidized3,4-isoprene monomer units result. This is an example of structure 2where R₂ is CH₃ and R₁═R₃═R₄═hydrogen.

The above polymers lack active protons and, prior to the inventiondescribed in application Ser. No. 08/081,950, had not been consideredcrosslinkable with amino resins. These polymers may be crosslinked withthemselves or with other polymers of the type described herein. They mayalso be crosslinked with polymers that are normally crosslinkable withamino resins such as polyesters, “advanced” epoxy resins (which possesssecondary alcohol groups), acrylics, alkyds, polyurethanes, etc.

The crosslinking agents which are useful in the present invention areaminoplasts. For the purposes of this invention, an aminoplast is aresin made by reaction of a material bearing NH groups with a carbonylcompound and an alcohol. The NH bearing material is commonly urea,melamine, benzoguanamine, glycoluril, cyclic ureas, thioureas,guanidines, urethanes, cyanamides, etc. The most common carbonylcomponent is formaldehyde and other carbonyl compounds include higheraldehydes and ketones. The most commonly used alcohols are methanol,ethanol, and butanol. Other alcohols include propanol, hexanol, etc.American Cyanamid (renamed CYTEC) sells a variety of these aminoplasts,as do other manufacturers. American Cyanamid's literature describesthree classes or “types” of aminoplasts that they offer for sale.

where Y is the material that bore the NH groups, the carbonyl source wasformaldehyde and R is the alkyl group from the alcohol used foralkylation. Although this type of description depicts the aminoplasts asmonomeric material of only one pure type, the commercial resins exist asmixtures of monomers, dimers, trimers, etc. and any given resin may havesome character of the other types. Dimers, trimers, etc. also containmethylene or ether bridges. Generally, type 1 aminoplasts are preferredin the present invention.

The aminoplast must be compatible with the epoxidized polymer. Acompatible aminoplast is defined as one which gives a phase stable blendwith the epoxidized polymer at the desired concentration and at thetemperature to which the mixture will be heated when the dispersion inwater is actually being made. We have found that it is best that theaminoplast be butylated to a significant extent for proper compatibilitywith the epoxidized polymers, i.e., the R groups must be butyl groups orat least primarily butyl groups.

For example, the following type 1 aminoplasts can be used to achieve thepurpose of the present invention: CYMEL 1156—a melamine-formaldehyderesin where R is C₄H₉, CYMEL 1170—a glycoluril-formaldehyde resin whereR is C₄H₉, CYMEL 1141—a carboxyl modified amino resin where R is amixture of CH₃ and i-C₄H₉, and BEETLE 80—a urea-formaldehyde resin whereR is C₄H₉. All of these products are made by American Cyanamid Companyand are described in its publication 50 Years of Amino Coating Resins,edited and written by Albert J. Kirsch, published in 1986 along withother amino resins useful in the present invention.

CYMEL 1170 is the following glycoluril-formaldehyde resin where R isC₄H₉:

Another is BEETLE® 80 urea-formaldehyde resin where R is C₄H₉ whoseideal monomeric structure is depicted:

Since there are little or no other functional groups, such as hydroxyl,amine, mercaptan or carboxyl groups, in the epoxidized polymers whichare cured according the present invention, the conventional mechanism bywhich these aminoplasts cure functionalized polymers cannot be used toexplain the reaction in the present system. A hypothesis which we putforth as a theory herein is discussed in detail in the aforementionedcopending application Ser. No. 08/081,950 which is herein incorporatedby reference.

In the crosslinkable waterborne dispersion, the epoxidized polydieneblock polymer should comprise from 10 to 65% by weight (% w) of thetotal dispersion. The aminoplast should be used in a ratio of 98:2 to60:40 by weight with the epoxidized polymer. Thus, the aminoplast willcomprise from 0.2 to 25% w of the dispersion. The dispersion will alsorequire a surfactant, preferably an amine salt of an acid. Thesurfactant is used in an amount from 0.1 to 10% w.

If less than 10% w of the polymer is used, then the solids content ofthe dispersion will be uneconomically low and if more than 65% w isused, then the viscosity of the dispersion (if it can be made at all)will be too high. If less than 0.2% w of the amino resin is used, thenthe composition will not crosslink and if more than 25% w is used, thencompatibility with the epoxidized polymer will be poor and poor qualitycured films will result. If less than 0.1% w of the surfactant is used,then stable dispersions in water cannot be made and if more than 10% wof the surfactant is used, then cured films will have high moisturesensitivity. The balance of the dispersion is water.

Since the epoxidized polydiene polymer and its mixtures with melamineresin are hydrophobic and insoluble in water, a surfactant must be usedto form a stable dispersion of the polymer and melamine in water. A widevariety of nonionic and anionic surfactants would be suitable. There arealmost no restrictions on the type of nonionic surfactant which could beconsidered. The only restriction on the type of anionic surfactant isthat the cation used to neutralize the acid on the hydrophobe must bevolatile enough to leave the film during the melaniine cure. Otherwise,a nonvolatile cation would neutralize the strong acid needed to catalyzethe melamine curing reaction, thereby inhibiting cure. In fact, thepreferred anionic surfactant is the one made by neutralizing the strongacid needed to catalyze the curing reaction with a volatile amine. Theamine-neutralized acid serves as the surfactant stabilizing thedispersion and then, after the film is cast, the amine volatilizes,regenerating the acid which catalyzes the melamine cure.

Surfactants are molecules which have a hydrophobic portion (A) and ahydrophilic portion (B). They may have the structure A—B, A—B—A, B—A—B,etc. Typically, the hydrophobic section can be an alkyl group (e.g.C₁₂), an alkyl/aryl group (e.g. octylphenol), a polypropylene oxideblock, a polydimethylsiloxane block or a fluorocarbon. The hydrophilicblock of a nonionic surfactant is a water soluble block, typically apolyethylene oxide block or a hydroxylated polymer block. Thehydrophilic block of an anionic surfactant is typically an acid groupionized with a base. Typical acid groups are carboxylic acids, sulfonicacids or phosphoric acids. Typical bases used to ionize the acids areNaOH, KOH, NH₄OH and a variety of tertiary amines, such as triethylamine, triisopropyl amine, dimethyl ethanol amine, methyl diethanolamine and the like. Nonvolatile bases such as NaOH and KOH should beavoided in this invention since they will neutralize the strong acidneeded to catalyze the melamine curing reaction.

A proton-donating acid catalyst is required to achieve the purposes ofthe present invention, i.e., crosslink the polymer using the aminoplastsdescribed above. It is normal that the amount of the acid catalyst usedrange from about 0.1 to about 4% w of the polymer/amine resin mixture tobe certain there is sufficient acid but an excess can be undesirable.Most preferably, from about 0.5 to about 2% w of the polymer/amine resinis used. The presence of a strong proton-donating acid is normallyrequired to catalyze the crosslinking reaction of many aminoplasts whichare useful in the present invention. However, some medium strength andeven relatively weak acids may also be effective depending upon theaminoplasts used. Generally, the most active catalyst are those with thelowest pKa values. The following list of acid catalysts which may beused in the present invention is arranged according to increasing pKavalue: mineral acids, Cycat® 4040 catalyst (p-toluene sulfonic acid),Cycat® 500 catalyst (dinonylnaphthalene disulfonic acid), Cycat® 600catalyst (dodecyl benzene sulfonic acid), oxalic acid, maleic acid,hexamic acid, phosphoric acid, Cycat® 296-9 catalyst (dimethyl acidpyrophosphate), phthalic acid and acrylic acid (copolymerized inpolymer). Other acids which may be used are described in theaforementioned American Cyanamid Company publication. Also, 3M BrandResin Catalyst FC-520 (diethylammonium salt of trifluoromethane sulfonicacid) may be used. Cycat® 600 was found to be a very useful catalyst.

It is highly preferred that the acid which is used in the surfactant bean acid which is capable of catalyzing the crosslinkling of the polymerand the aminoplasts. Such acids are described above and include thevarious sulfonic acids described in the preceding paragraph. After thedispersion is applied to a substrate, usually after being formulated fora specific application such as a coating, adhesive or sealant, thevolatile amine in the surfactant will evaporate into the atmosphere,freeing the acid to catalyze the curing reaction between the amino resinand the epoxidized polymer. This is highly advantageous because iteliminates the cost of adding separate surfactant and acid catalystcomponents to the process for making these dispersions and also becauseit is a very simple and very effective approach to preparing dispersionsin water. However, it is within the scope of this invention to use anonionic or anionic surfactant to make the dispersion of epoxidizedpolymer/aminoplast which does not utilize the amine salt of the acidwhich can catalyze the curing reaction. In this case, of course, theacid catalyst would then have to be added to the dispersion.

The curing generally occurs within 5 seconds to 60 minutes, preferably10 to 30 minutes, once the polymer and aminoplast are exposed to thecatalyst and usually high temperature. However, curing could occur atnear ambient temperature over a period of up to 60 days such as forconstruction mastics, laminating adhesives and flexible packaginglaminating adhesives.

The cure temperature generally ranges from −5° C. to 400° C. 100 to 300°C. is preferred and 100 to 200° C. is most preferred. In someapplications, such as coil coating, curing is accomplished throughheating to a maximum substrate surface temperature of up to 300° C. Ifthis cure schedule is used, the time at this temperature is generallyvery short (on the order of 5 seconds) and cure continues as the surfacecools.

Premature crosslinking is prevented by blocking the acid catalyst as anamine salt. The most preferred amine used in this work is triethylamine.Other blocking agents include triisopropylamine, dimethylethanolamine,methyldiethanolamine, diethyl-ethanolamine, triethanolamine,diisopropanolamine, morpholine and 2-amino-2-methyl-1-propanol, water,primary, secondary and tertiary alcohols, as well as others described inthe aforementioned American Cyanamid Company publication.

One method for maldng the dispersions of the present invention is thewater-continuous process. In this process, the epoxidized polymer andthe amino resin, heated to reduce viscosity so it can be handled easily,usually to about 25 to about 80° C., are added to a hot water solutionof the surfactant and dispersed preferably under high shear conditions.This process is easy to use because the viscosity is always low sincewater is always the continuous phase.

Dispersions according to the present invention can also be made by theinversion process. In this process, the epoxidized polymer and the aminoresin are mixed at about 25 to about 90° C. with, for example, a stirrercomposed of two 4-blade propellers on a shaft rotating at about 500 to5000 rpm. Water is added slowly over a period of at least 15 minutes.The mix is organic-continuous initially. As water is slowly added, theviscosity increases. The viscosity becomes very high as the inversionpoint is approached. As more water is added, the dispersion inverts fromorganic-continuous to water-continuous and the viscosity dropsdramatically. This process is preferred over the water-continuousprocess because it usually gives a better, smaller particle size, morestable dispersion.

The present invention has many advantages. The main advantage is thatthe products can be applied at ambient temperatures as low viscosityliquids without the use of large quantities of solvents. Anotheradvantage is that it avoids the problem of radiation curing whichprimarily is the cost of the expensive equipment or formulationingredients required for such crosslinkling. The present invention alsoavoids the problems associated with radiation cure of coatings onirregularly-shaped objects. The waterborne dispersions can also be usedas additives to other waterborne polymers having compatible surfactantsystems to enhance specific properties such as toughness andflexibility.

The crosslinked materials of the present invention are useful inadhesives (including pressure sensitive adhesives, contact adhesives,laminating adhesives and assembly adhesives), sealants, coatings, films(such as those requiring heat and solvent resistance), printing plates,fibers, and as modifiers for polyesters, polyethers, polyamides andepoxies. In addition to the epoxidized polymer and any curing aids oragents, products formulated to meet performance requirements forparticular applications may include various combinations of ingredientsincluding adhesion promoting or tackifying resins, plasticizers,fillers, solvents, stabilizers, etc.

Adhesive compositions of the present invention may be utilized as manydifferent kinds of adhesives, for example, laminating adhesives,flexible packaging laminating adhesives, pressure sensitive adhesivesand tie layers. The adhesive can consist of simply the epoxidizedpolymer or, more commonly, a formulated composition containing asignificant portion of the epoxidized polymer along with other knownadhesive composition components.

One preferred use of the present formulation is the preparation ofpressure-sensitive adhesive tapes and labels. Normally, the polymerdispersions of this invention win be mixed with a dispersion of acompatible tackifying resin prior to application to the backing. Thepressure-sensitive adhesive tape comprises a flexible backing sheet anda layer of the adhesive composition of the instant invention coated onone side of the backing sheet. The backing sheet may be a plastic film,paper or any other suitable material and the tape may include variousother layers or coatings, such as primers, release coatings and thelike, which are used in the manufacture of pressure-sensitive adhesivetapes. Alternatively, when the amount of tackifying resin is near zero,the compositions of the present invention may be used for a sizing agentor saturant for paper, fabric or other fibers and for toughening asphaltand the like.

Another preferred use of the present formulation is the preparation ofcoatings for substrates that can be baked at the temperatures describedabove. Such coatings are expected to be of particular importance forautomotive and general metal finishes, especially coil coats. As will beseen in the following examples, coatings can be prepared with excellentcolor, clarity, hardness and adhesion. If substantially saturatedpolymers are used, the weatherability of the resulting films is expectedto be excellent.

EXAMPLES

Two epoxidized polymers were used to demonstrate this invention. PolymerA was a 6000 molecular weight (MW) triblock polymer having 1000 MWpolyisoprene blocks on both ends of a center block composed of a randomcopolymer of polystyrene (2500 MW) and hydrogenated polybutadiene (1500MW). The polymer was epoxidized to 1.2 milliequivalents (meq) of theepoxy per gram of polymer (meq/g). Polymer B was a 6000 MW diblockpolymer having a 1000 MW polyisoprene block and a 5000 MW polybutadieneblock. The polymer was epoxidized to 4.8 meq/g. The acid used was CYCAT600, dodecyl benzene sulfonic acid (a 70% weight solution in isopropylalcohol). Ammonia (NH₃) or triethylamine (TEA) was used to neutralizethe acid. Three melamine resins were tested in the formulation, a fullymethylated melamine (CYMEL 303), a fully butylated melamine (CYMEL1156), and an acid functional, methylated/butylated melanine (CYMEL1141). A silicone antifoam (BYK-034) was used in formulations wherefoaming was a problem.

Two processes were used to prepare the dispersions; the water-continuousprocess and the inversion process. In the water-continuous process, theorganic part of the formulation, heated to about 80° C., was added tohot water containing the CYCAT 600/amine surfactant and was dispersed inthe soapy water using a Silverson high shear mixer/emulsifier. In theinversion process, the organic part of the formulation was mixed in acan at about 80° C. with a stirrer composed of two 4-blade propellers onthe shaft, rotating at about 2000 rpm. Water was added slowly over abouta 30 minute period. Of course, the mix was organic continuous initially.As water was slowly added, viscosity increased. Viscosity became veryhigh as the inversion point was approached. As more water was added, thedispersion inverted from organic-continuous to water-continuous and theviscosity dropped dramatically. The compositions of the dispersions madein this work with Polymer A are shown in the table.

Example 1

The simplest dispersion (Composition #1) consists of Polymer A dispersedin water containing the surfactant (CYCAT 600/NH₃) and antifoam(BYK-034). When made by the inversion process, this gave a nice, lowviscosity, milky white dispersion. Since this dispersion contains nocrosslinker, films cast on a substrate dry clear and glossy but they aresticky. This dispersion could have utility as an additive to other waterbased products with which it could cocure. Although difficult, it may bepossible to add a melamine curing resin to this dispersion of polymer inwater, thereby giving a product which would crosslink.

Example 2

A better approach to a dispersion which would cure is to make a premixof the melamine and the polymer together before dispersing this premixin water to insure intimate mixing of the polymer and crosslinker. Todetermine the feasibility of this approach, three melamine resins, CYMEL303, 1141 and 1156, were melt mixed manually with Polymer A at about100° C. in a 20/80 ratio by weight of resin/polymer. It was found thatCYMEL 1141 and 1156 gave homogeneous blends but the blend with CYMEL 303phase separated upon cooling to room temperature and standing overnight.The incompatibility with CYMEL 303 is surprising since CYMEL 303 was aneffective crosslinker for Polymer A when films were cast from solventsolution.

Attempts were made to prepare dispersions of Polymer A with each of thethree CYMEL resins. Good dispersions could be made using CYMEL 1141 and1156. However, as shown by Compositions #2, #3 and #4, attempts atdispersing Polymer A/CYMEL 303 blends in water were unsuccessful, evenwhen a coalescing solvent, ethylene glycol monobutyl ether (BUTYLOXITOL) was present.

Since CYMEL 1141 contains some acid functionality, it probably aidsformation of the dispersions. Using NH₃ to neutralize CYCAT 600 and theacid groups on CYMEL 1141, a nice dispersion of 80/20 by weight PolymerA/CYMEL 1141 was formed with the Silverson (Composition #5). An attemptto make this same dispersion by the inversion process was unsuccessful(Composition #6). As water was added, the mix became so thick that itclimbed out of the can as the stirrer attempted to mix it. It was foundthat addition of BUTYL OXITOL was effective in reducing the viscosity ofthe mix enough that good dispersions could be made by the inversionprocess. The dispersion using 10% by weight BUTYL OXITOL (Composition#7) looked nice originally but coagulated upon storage at roomtemperature for 3 months. The dispersion using 20% by weight BUTYLOXITOL (Composition #8) creamed but remained dispersed upon storage.Using TEA to neutralize the acid, a nice dispersion was made with only10% by weight BUTYL OXITOL (Composition #9) and this dispersion remainedunchanged upon storage for 3 months at room temperature.

Films of Compositions #8 and 9 were drawn down on aluminum panels (A412Q-panels) with a #52 wire wound rod. After drying overnight at ambientconditions, the films were smooth and coherent, and they were tackybecause uncured Polymer A is very tacky. Surprisingly, when baked, filmsof Composition #8 did not cure, even after 30 minutes at 200° C.However, films of Composition #9 did cure to give non-tacky films aftera 15 minute bake at 200° C. These cured films of Composition #9 werefairly dull and hazy suggesting at least partial incompatibility betweenthe melamine and Polymer A when they begin to cure.

Example 3

To minimize this partial incompatibility of Polymer A and CYMEL 1141,the polymer and melamine were partially reacted prior to dispersing themin water. Enough reaction must be accomplished that Polymer A and CYMEL1141 are compatible during cure but too much reaction will cause the mixto be high in viscosity, making inversion to the water dispersiondifficult. The procedure used to prepare Composition #10 wassatisfactory.

In the procedure to make Composition #10, 80 parts by weight (pbw)Polymer A, 20 pbw CYMEL 1141, and 18 pbw BUTYL OXITOL were heated to 80°C. in a resin kettle. While stirring, 0.4 pbw CYCAT 600 diluted with 2pbw BUTYL OXITOL was added and the mixture was cooked for 2 hours. Thesurfactant was prepared by mixing 1.6 pbw CYCAT 600 and 2 pbw TEA in abottle with 5 pbw water. This surfactant was added to the partiallyreacted Polymer A/CYMEL 1141 at 70° C. while stirring at 2,000 rpm witha stirrer having dual 4-bladed propellers. Blowing ambient temperatureair on the can helped control the temperature rise due to viscousheating. Deionized water was then slowly added.

Since some of the volatile TEA was lost during the dispersion, 2% byweight TEA was in the water being added to the mix in order to maintaina pH of at least 9. If the water was added too quickly (in less thanabout 5 minutes), a dispersion was obtained which creamed upon standingovernight (probably because the particle size was too large). However,if the water was added over about a 15 to 30 minute period, a very nicedispersion which did not change with storage, was obtained. Inversionoccurred after adding about 100 pbw of water but the viscosity was stillquite high. For Composition #10, more water was added until theviscosity became fairly low. Excluding the water, Composition #10contains about 79% w solids and 21% w solvent. Films of Composition #10on aluminum cured well when baked 20 minutes at 175° C. to giveexcellent non-tacky, clear, colorless, glossy, coherent coatings.

Formulations for Dispersions of Polymer A in Water Composition, pbw 1 23 4 5 6 7 8 9 10 Polymer A 100 80 80 80 80 80 80 80 80 80 CYMEL 303 2020 20 CYMEL 1141 20 20 20 20 20 20 CYCAT 600  2 2.5 2.5 2.5 2.5  2  2  2 2  2 NH3 0.9 1.1 1.1 1.1 1.0 0.9 0.9 0.9 TEA  2  2 BYK-034 0.1 0.1 0.10.1 0.1 0.1 0.1 0.1 0.1 BUTYL OXITOL 10 20 10 20 10 20 Deionized Water100  100  100  100  100  100  100  100  100  165  Dispersion Inv Sil InvInv Sil Inv Inv Inv Inv Inv Process¹ Dispersion nice fail fail fail nicefail³ very nice very very Appearance nice nice nice Storage Stability²nice coag. nice, nice very creamed nice ¹Dispersion Process: Inv =inversion process, Sil = water-continuous process with Silverson mixer.²Storage Stability: Appearance of dispersion after storage at ambientconditions for up to 3 months. ³Mixture thickened when water was addedand became so thick it climbed out of can.

Example 4

A dispersion of Polymer B was prepared following the same procedure usedto disperse Composition #10 in water. The procedure worked very well,resulting in a low viscosity, milky white dispersion which remainedstable upon storage showing no coagulation or phase separation. Films ofthis dispersion of Polymer B cast on aluminum and baked 20 minutes at175° C., were hard, clear, glossy coatings having a pale yellow color.

We claim:
 1. A coating formed by crosslinking a waterborne dispersion which is applied to a substrate, said waterborne dispersion comprising: (a) 10 to 65% by weight of a polydiene block polymer having a weight average molecular weight of from 2000 to 3,000,000 and containing at least five olefinic epoxy groups per molecule which are sterically hindered; (b) 0.2 to 25% by weight of a compatible aminoplast; (c) 0.1 to 10% by weight of a surfactant which is nonionic or anionic and has a volatile cation; (d) 0.1 to 4% by weight of a proton-donating acid catalyst; and (e) water.
 2. The coating of claim 1, wherein the aminoplast is a butylated aminoplast.
 3. The coating of claim 1, wherein the acid is an acid which catalyzes crosslinking of the polymer and the aminoplast.
 4. The coating of claim 1, wherein the amine is a tertiary amine selected from the group consisting of triethylamine, triisopropylamine, methyidiethanolamine and dimethylethanolamine.
 5. The coating of claim 1, wherein the surfactant is an amine salt of an organic acid.
 6. The coating of claim 1, wherein the water is present in the waterbome dispersion at a weight ratio of the water to the polydiene block polymer ranging from 100:80 to 165:80.
 7. An adhesive formed by crosslinking a waterbome dispersion which is applied to a substrate, said waterbome dispersion comprising: (a) 10 to 65% by weight of a polydiene block polymer having a weight average molecular weight of from 2000 to 3,000,000 and containing at least five olefinic epoxy groups per molecule which are sterically hindered; (b) 0.2 to 25% by weight of a compatible aminoplast; (c) 0.1 to 10% by weight of a surfactant which is nonionic or anionic and has a volatile cation; (d) 0.1 to 4% by weight of a proton-donating acid catalyst; and (e) water.
 8. The adhesive of claim 7, wherein the aminoplast is a butylated aminoplast.
 9. The adhesive of claim 7, wherein the surfactant is an amine salt of an organic acid.
 10. The adhesive of claim 7, wherein the acid is an acid which catalyzes crosslinking of the polymer and the aminoplast.
 11. The adhesive of claim 7, wherein the amine is a tertiary amine selected from the group consisting of triethylamine, triisopropylamine, methyidiethanolamine and dimethylethanolamine.
 12. The adhesive of claim 7, wherein the water is present in the waterbome dispersion at a weight ratio of the water to the polydiene block polymer ranging from 100:80 to 165:80.
 13. A sealant formed by crosslinking a waterbome dispersion which is applied to a substrate, said waterbome dispersion comprising: (a) 10 to 65% by weight of a polydiene block polymer having a weight average molecular weight of from 2000 to 3,000,000 and containing at least five olefinic epoxy groups per molecule which are sterically hindered; (b) 0.2 to 25% by weight of a compatible aminoplast; (c) 0.1 to 10% by weight of a surfactant which is nonionic or anionic and has a volatile cation; (d) 0.1 to 4% by weight of a proton-donating acid catalyst; and (e) water.
 14. The sealant of claim 13, wherein the aminoplast is a butylated aminoplast.
 15. The sealant of claim 13, wherein the surfactant is an amine salt of an organic acid.
 16. The sealant of claim 13, wherein the acid catalyzes crosslinking of the polymer and the aminoplast.
 17. The sealant of claim 13, wherein the amine is a tertiary amine selected from the group consisting of triethylamine, triisopropylamine, methyidiethanolamine and dimethylethanolamine.
 18. The sealant of claim 13, wherein the water is present in the waterbome dispersion at a weight ratio of the water to the polydiene block polymer ranging from 100:80 to 165:80. 